Metal-semiconductor rectifying elements, usually referred to as Schottky diodes, are used extensively in bipolar integrated circuits (IC's). In making a Schottky diode, a partly finished IC having an N-type semiconductive region that acts as the cathode is typically placed in a deposition chamber whose pressure is reduced to a very low level. A metal or metallic alloy is evaporatively deposited on the N-type region. The resulting metallic layer is then selectively etched to divide it into a number of separated segments. One of these is the anode that forms a rectifying junction with a portion of the N-type region. Another of the metallic segments is the cathode contact which ohmically adjoins another portion of the N-type region more highly doped than the first-mentioned portion.
The voltage V.sub.F between the anode and the cathode contact when the rectifying junction is forwardly conductive characterizes a Schottky diode for many applications. Muller et al, Device Electronics for Integrated Circuits (John Wiley & Sons, New York: 1977), Chap. 2, discusses various factors that affect V.sub.F. For example, V.sub.F differs from one metal or metal-like substance to another. The net concentration of the N-type dopant on the semiconductive side of the rectifying junction affects the forward voltage. These factors provide wide latitude in selecting materials to optimize V.sub.F.
For some types of Schottky diodes such as aluminum-silicon Schottkies, V.sub.F at a particular diode location in an IC often differs significantly from IC's processed together in one batch to IC's processed together in another batch. This variation is usually undesirable. It can lead to markedly reduced performance or device failure. Attempts to minimize V.sub.F variation by keeping the metal deposition system clean have had only marginal success with aluminum-silicon Schottky diodes. For such types of Schottkies, it is desirable to ascertain processing factors that influence the forward voltage so that its value can be better controlled from IC to IC.